Asexual Reproduction inEukaryotes: MitosisThe Argentine bandThe real thing goingon inside their cellsNuclear Genomes and ChromosomesGenome size in bp (or kbp or Mbp or Gbp) = C value S. cerevisiae Homo sapiensC 12.5 Mbp 3.3 GbpNumber genes 5,770 20,000 - 25,000 (or even 65,000?)Number of chromosomes in a haploid set = N Diploids have 2N chromosomesDrosophila 4Yeast 16Humans 23Dogs 39Human chromosome size ranges 49 Mbp - 246 Mbp ≈ 1.6 - 8.2 cmSmallest is longer than entire cell.Total ≈ 1 mGo to http://www.ncbi.nlm.nih.gov/mapview/map_search.cgiClick on the number below any chromosome; 22 might be best because it issmallest.Chromosome Structure and KaryotypesBasic chromosome structureConventional diagram of metaphasechromosome with 2 chromatids.Centromere = DNA sequencewhere proteins bind to make akinetochore = structure to whichmicrotubules bind.Left: human metaphasechromosomes squashed andstained to show landmarksRight: diagram of humankaryotype with G-bands. Short(p) and long (q) arms.Eukaryotic Cell CycleG1SG2 G1 + S + G2 = interphaseMitosisCell CycleVariable lengths. Total time 15 m inutes --> daysAnimal cells in culture ca. 1 dayG1 G2Diploid cell 2C  4C C = amount of DNA2N  4NHaploid cell C  2C N  2N chromosomes  chromatidsEach eukaryotic chromosome replicates once and only once in each cell cycle.Replication origins are caused to fire in S phase, then are prevented from re-initiating. Block to reinitiation is removed at mitosis.Cytokinesis (cell division)Mitosis Diagrams 1Karyotype: N = 21 short acrocentric chromosome1 long metacentric chromosomeGene A is on metacentric, gene B is on acrocentric chromosome.Cell is heterozygous: A a, B bNuclear membrane may or may not break down, dependng on the species.centrioleMitosis Diagrams 2In mitosis:Sister kinetochores (centromeres) are attached to microtubules fromopposite poles in metaphase, therefore sister kinetochores and sisterchromatids segregate at anaphase, therefore daugher cells get one copy ofeach chromosome.MitosisImagesMany organisms are haploid during part or all of their life cycle:e.g.ferns, many unicellular protists, fungi. These includeimportant experimental organisms.Mitosis works the same way in haploid as in diploid cells,except that there is only one set of chromosomes.Eukaryotic ClonesClone = all descendants of a single cell by mitosis.Asexual reproduction.Seen in:(1) Unicellular organisms (e.g. yeast, Chlamydomonas): progeny of single cell.Handle like bacteria.(2) Multicellular organisms (e.g. animal, plant):(a) all cells in one individual(b) monozygotic twins, etc.(c) progeny produced by fission (planaria) or budding (Hydra)(d) progeny produced by vegetative propagation of plants (aspen)(e) progeny produced by some kinds of parthenogenesis (some fish, lizards,Drosophila; many plants)Parthenogenesis = egg develops into an adult without fertilization. Some forms ofparthenogenesis produce diploid egg by mitotic division; others do it by meioticdivision followed by restoration of diploidy by various means. All usually calledasexual.Many eukaryotes are asexualMany parasites are asexualSome Asexual EukaryotesToday much genetic analysis is done with cells or organisms reproducing asexually.Used for:• Selecting mutants.• Making custom-made mutants by transformation/transfection.• Growing identical organisms that can be used to separate effects ofgenotype from environment, etc.Modern genetic methods might allow one to use a clone for other purposes. So far, this one isimpossible:Verse by Isaac Asimov, meant to be sung to tune of "Home on the Range""O give me a cloneOf my own flesh and boneWith its Y chromosome changed to X.And when it is grownThen my own little cloneWill be of the opposite sex.Clone, clone of my own,With its Y chromosome changed to X.And when I'm aloneWith my own little cloneWe'll both think of nothing but ---."Summary1. In the cell cycle, each chromosome = DNA molecule is replicated exactly once.2. In anaphase of mitosis, sister centromeres (kinetochores), and hence sister chromatids,segregate. Thus each daughter cell gets one copy of each chromosome.Consequence:Daughter cells produced by mitosis have identical chromosomes.Genes are identical, barring mutation.Cells and organisms produced by mitosis constitute a clone.Today much genetic analysis is done with cells or organisms reproducing asexually.BacteriaYeastChlamydomonasAnimal (including human) and plant cells in cultureUsed to:Select and identify mutants.Custom-made mutants:Transform/transfect cells: get them to take up a piece of a gene with a mutation built into it.That piece of DNA replaces the resident gene, which is now